1. Submersible reef pump - this pump sits inside the sump under water. It is commonly used when there is little or not enough room for a pump to be installed externally under a stand etc.

2. In-line external reef pump - this pump sits outside & next to the sump & is connected to the sump by means of a bulkhead installed in the side of the sump. There are other ways to connect these pumps to a system but for the simplest application & for my system we will focus on this method of connection.